1. Field of the Invention
The present invention relates to a semiconductor pressure sensor which measures pressure, such as atmospheric pressure.
2. Description of the Related Art
A diaphragm type semiconductor pressure sensor is known as a semiconductor pressure sensor which measures the tire pressure of a vehicle or the like. Generally, the diaphragm type semiconductor pressure sensor includes a semiconductor substrate having a diaphragm and a cavity for pressure detection on its top and bottom surfaces, respectively, and a base substrate bonded to the semiconductor substrate so as to seal the cavity, and has a rectangular sectional shape in which the cavity is formed by vertically cutting the surface of the semiconductor substrate. A plurality of piezoresistors (pressure-sensitive resistors) is disposed on each side of the diaphragm, and the midpoint electric potential of a bridge circuit formed by the plurality of piezoresistors is output as a pressure measurement voltage. For example, the diaphragm is distorted when the pressure is applied from the diaphragm side of the semiconductor substrate, and the resistance of the piezoresistor changes according to the degree of distortion. As a result, since the midpoint electric potential of the bridge circuit changes, the pressure can be measured on the basis of the midpoint electrical change.
In such a semiconductor pressure sensor, the diaphragm-side surface of the semiconductor substrate becomes a circuit surface including a portion of circuit wiring to piezoresistors, electrode pads, and the like. In this case, it is known that the device sensitivity can be adjusted by reducing the thickness of a protective film, which insulates and protects the circuit surface, on the diaphragm. JP-A-2000-356560 discloses a configuration in which the thickness of a surface oxide film 7 as a protective film is set to be small on a gauge resistor 5.